The invention relates to a controller for valve mechanism of a brake booster, and more particularly, to such controller capable of reducing a play or an ineffective stroke during a brake operation to thereby improve a brake feeling.
In a brake booster, the opening or closing of a valve mechanism is controlled by an operating rod which is mechanically interlocked with a brake pedal. During a brake operation, the atmospheric pressure is introduced into a rear power chamber to apply a pressure differential between the rear and the front power chamber to a power piston, thus obtaining a booster function. When the brake is released, the rear power chamber is interrupted from communication with the atmosphere and is brought into communication with the front power chamber, thus allowing the power piston to be returned to its inoperative position under the bias of a return spring. To improve the response of a brake booster, it is preferred to increase the cross-sectional area of a flow path between the rear power chamber and the atmosphere and between the both power chambers, or to increase the lift of the valve mechanism. However, when the lift of the valve mechanism is increased in order to achieve an increased area of the flow path between the both chambers, there results an increase in the play or ineffective stroke of a brake pedal which is required when the brake pedal is depressed from its inoperative condition to cause the valve mechanism to interrupt the communication between the both power chambers. In other words, the brake feeling is degraded.
To overcome this difficulty, there is known a controller for valve mechanism in which the operating rod is provided with a stop member so that during the time when the power piston is returning to its original inoperative position after the brake pedal is released from the brake operated position, the increased lift establishes an increased cross-sectional area until the power piston reaches its inoperative position, whereupon the stop member integral with the operating rod bears against a stop which is provided outside a closed shell to thereby prevent the operating rod from moving rearward freely, thus maintaining the operating rod at an advanced position relative to the power piston during the non-operated condition and thus maintaining a small lift.
However, in this arrangement, the stop member must be located on the operating rod on a portion thereof which projects out of the power piston and the stop which is provided for abutment against the stop member must be disposed on the exterior of the closed shell. This resulted in an increased size of the brake booster, defeating a compliance with the recent trend toward an arrangement of a reduced weight and size.